Forklift truck with swinging mast

ABSTRACT

The specification describes a forklift truck having a mast structure which is mounted for swiveling about an axis offset to one side of the fore-and-aft extending center line of the truck between a forwardly facing position and a sideways facing position. The mast structure comprises a first guide which is fixed against movement in a vertical direction, a second guide which is guided for movement up and down along the first guide, a carrier frame supporting a load fork and guided for movement up and down along the second guide, and a single-extension jack for actuating the movement of the second guide and of the carrier frame. The connections between the jack and the second guide and between the second guide and the carrier frame are such that the speed of the second guide along the first guide is twice the speed of the jack and that the speed of the carrier frame along the second guide is twice the speed of the second guide along the first guide.

United States Patent [72] inventor James William Henry Taylor New Addington, England [21] Appl. No. 734,169 [22] Filed June 3, 1968 [45] Patented Sept. 28, 1971 [73] Assignee Matbro Limited Horley, Surrey, England [32] Priority June 5, 1967 [33] Great Britain [31 25923/67 [54] FORKLIFT TRUCK WITH SWINGING MAST 3,344,941 10/1967 Mathew etal.

" 3 ,39S ,8 D 33/1968 Mathew et a1. 214/671 X FOREIGN PATENTS 764,982 l/l957 Great Britain 187/9 Primary ExaminerGerald M. Forlenza Assistant Examiner-Raymond B. Johnson Attorneywenderoth, Lind & Ponack ABSTRACT: The specification describes a forklift truck having a mast structure which is mounted for swiveling about an axis offset to one side of the fore-and-aft extending center line of the truck between a forwardly facing position and a sideways facing position. The mast structure comprises a first guide which is fixed against movement in a vertical direction, a second guide which is guided for movement up and down along the first guide, a carrier frame supporting a load fork and guided for movement up and down along the second guide, and a single-extension jack for actuating the movement of the second guide and of the carrier frame. The connections between the jack and the second guide and between the second guide and the carrier frame are such that the speed of the second guide along the first guide is twice the speed of the jack and that the speed of the carrier frame along the second guide is twice the speed of the second guide along the first guide.

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FORKLIFT TRUCK WITH SWHQGING MAST The present invention relates to lift trucks and in particular to lift trucks of the type in which the mast swings about a vertical axis to permit the load to be carried lengthwise of the machine. Such machines are advantageous particularly for handling timber, steel girders and similar long loads.

According to this invention there is provided a lifttruck having a mast structure which is mounted for swiveling about an axis offset to one side of the fore-and-aft extending centerline of the truck between a forwardly facing position and a sideways facing position, such that in both of said positions of the mast structure the center of gravity of a load carried by the mast structure is disposed on or close to said centerline, said mast structure comprising a first guide which is fixed against movement in a vertical direction, a second guide which is guided for movement up and down along the first guide, a carrier frame which is guided for movement up and down along the second guide, and a single-extension jack for actuating the movement of the second guide on the first guide and of the carrier frame along the second guide, the connections between the jack and the second guide and between the second guide and the carrier frame being such that the speed of the second guide along the first guide is twice the speed of the jack and that the speed of the carrier frame along the second guide is twice the speed of the second guide along the first guide.

The mast structure is preferably adapted to swing rearwardly from said forwardly facing position to said sideways facing position, the mast structure being disposed, when in the sideways facing position, in a well between the front wheels of the truck. The front wheels may conveniently be interconnected by a conventional driving axle extending across the well, the foot end of the first guide terminating above the level of the axle.

According to a preferred feature of the invention, the truck has a deck on which a load carried by the carrier frame can be rested when the carrier frame is in said sideways facing position, which deck is at a level just above the tops of the front wheels.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawings, wherein:

FIGS. 1 and 2 are respectively front and side views of a slewing gate member for supporting the fixed and moving guides of the mast structure,

FIGS. 3 and 4 are respectively front and side views of the fixed and moving guide of the mast structure complete with the hoisting jack,

FIG. 5 shows a plan of the gate member and mast structure on the lift truck, and

FIG. 6 shows a side view of the front end of the truck showing the king post structure and the fixed guide of the mast structure.

Referring to FIGS. 1, 2, 5 and 6, a fabricated steel gate member 1 is supported on a lift truck chassis and carries a mast structure 12. The gate member 1 is provided with apertured tongues 2 for connection by pivot pins with a vertical king post structure 1a positioned to one side of the centerline of the lift truck. The centers of the apertures 3 in the tongues 2 thus define the slewing axis of the mast structure 12 of the lift truck.

The gate member is provided with an apertured lever are 1b for connection with the piston rod 4a of a slewing jack 4, the body of which is pivotally secured to a fixed pivot 40 on the frame of the lift truck. A pair of forwardly facing cheeks 5 are formed with trunnion apertures 6 for connection of the fixed guide of the mast structure 12. The fixed guide can be tilted about the common axis of a pair of pins which are mounted in the trunnion apertures 6 by means of tilt jacks 7, the bodies of which are pivotally connected to the gate member by trunnions 8.

The gate member 1 is also provided with a support roller 9 which runs on an arcuate track 10 centered on the axis of swing of the gate member and mast structure and mounted on the frame of the lift truck.

The position of the front axle is indicated at 11. The mast trunnion pins which are accommodated in apertures 6, and about which the mast structure tilts relative to the gate member, move in a horizontal plane at a position slightly above the level of the axle l1.

' The mast structure is shown in more detail in FIGS. 3 and 4 and comprises a fixed guide 21 and a moving guide 22. These guides are each formed of a pair of I-section beams, secured together by suitable crossmembers as explained below. In the present case the vertical I-beams of the moving guide 22 lie outwardly of those of the fixed guide 21, while the flanges of the beams of the moving guide 22 lie forwardly of the flanges of the fixed guide. In the fully lowered position of the mast, shown in FIGS. 3 and 4, the foot of the moving guide 22 extends to a considerably lower level than the fixed guide 21. At its foot end the fixed guide 21 is provided with trunnion mountings 23 in which are received the pivot pins mounted in the trunnion apertures 6 of the gate member 1 to provide a horizontal pivot about which the mast structure may be tilted.

A pair of yokes 24 are welded to the flanges of the beams for connection to the pistons of the tilt jacks 7. The foot end of the main hoist jack 25 is supported on trunnion pins 25 guide and acting on the forward flange of the beams of the moving guide to give the maximum stability when the moving guide is fully hoisted.

The beams of the moving guide are cross-connected by crossmembers 32 and 33 at the level of the. rollers 28 and 29 respectively. The upper crossmember 33 is in the form of a shaped plate, which is continued upwardly and carries a rearwardly projecting chain anchorage 34 at its top edge. At their top end the beams of the moving guide are connected by a top plate 35, which rests on the top of the fixed guide when the mast is fully lowered, and a torque tube 36 carried between rearwardly extending cheeks 36'. ,Chain pulleys 38 are mounted between the cheeks 36'.

The top end of the piston rod of the hoist jack 25 is provided with a yoke 39, supporting a shaft 40, on which a pair of chain pulleys 41 are mounted. Chains 42 are anchored at one end to fixed anchorages on the anchorage member 26 of the fixed guide 21, pass over the chain pulleys 41 and are anchored at their other ends to the chain anchorage 34. Thus, it will be understood that when the piston of the hoist jack 25 is extended, the moving guide 22 will rise at double the rate of jack extension. Thus, the single-extension jack (i.e., a jack in which the piston rod by a distance somewhat less than the overall length of the cylinder) can lift the extra length moving guide by its full amount. This is advantageous since telescopic lifting rams are relatively undesirable for lift trucks because of their relative complexity and relatively high initial cost and because they do not raise the load at constant rate.

The carrier frame 48 of the lift truck is guided in conventional manner on the moving guide 22 and is raised in the conventional manner by chains 50 passing over the chain pulleys 38 from fixed anchorages associated with the torque tube 27.

It is a particular advantage of the illustrated mast arrangement that in the fully lowered position there is a clear space between the top of the jack and the top of the moving guide, since the jack length is now little in excess of half the length of the moving guide, as compared with the conventional arrangement in which the top end of the hoist jack extends up to the top crossmember of the moving guide and lifts it by direct thrust. Such clear space greatly improves the field of vision of the driver, who is normally seated at a driving position at one side of the machine. The field of vision is particularly improved when the mast is in the forward facing position and the fork lift truck is moving forward with its forks lowered for insertion under a load to be hoisted and transported. It is at this point that the driver requires an optimum field of vision; when the mast is slued during travel the mast guides have much less obscuring effect.

The illustrated truck is well suited for carrying long loads such as timber and pipes. When the load fork or other carrier member (not shown) secured to the carrier frame has been engaged under the load, the mast structure being in its forwardly facing position as indicated in FIG. 5, the jack is operated to raise the moving guide clear of the front axle and to raise the carrier member clear of a flush deck 51 of the truck, jack 4 is operated to slew the gate member and mast structure rearward into the well formed between the front wheels of the truck to bring the mast structure into a sideways facing position. The carrier member is then lowered to rest the load on the deck unit while the vehicle carries the load to its destination.

In prior constructions where the moving guide moves at the same speed as the jack, by the time the foot of the moving jack has cleared the front axle, the load carrier is well above the deck, and much time is therefore wasted in subsequently lowering the load carrier on to the deck. Similarly more time is wasted when the load is to be put down.

It will be understood that the minimum height of the load supporting deck is governed by the diameter of the front wheels of the lift truck. Since the load must clear the front wheels, then the minimum height of the load-supporting deck from the ground is a little greater than the diameter of the front wheels. Since the front wheels of the lift truck are not themselves steerable in relation to the axle which supports them, the well in the forward part of the lift truck can be provided in the present construction within which well the lower end of the mast guides slues. It is thus possible to utilize a conventional driving axle for the front axle of the lift truck and to have the lower end of the fixed guide of the mast structure at a height slightly above the axis of the front wheels. In the fully lowered position the foot and of the moving guide of the mast has a ground clearance of 6-12 inches, as is conventional in fork lift trucks. It will thus be seen that by raising the moving guide to bring its foot end level with the foot end of the fixed guide to permit the mast to sine, the carrier frame and the load are hoisted by a double amount and will be slightly above the level of the front wheels. By careful arrangement of the relative levels of the load-supporting deck, the foot and of the fixed guide and the foot end of the moving guide and carrier frame in the fully lowered, ground-loading position, it will be seen that when the foot end of the moving guide has been raised sufficiently to permit the mast to slue, the carrier frame and load will be at a level slightly above the top of the front wheels and may thus be slued over the support deck and lowered directly onto the deck with a minimum of movement.

I claim:

1. A lift truck having a chassis, steerable wheels at one end of said chassis, a well at the other end of said chassis facing lengthwise of said truck, an axle extending across said well, driving wheels mounted on opposite ends of said axle, a deck extending along one side of said truck at a level just above the tops of said driving wheels, a mast structure mounted for swiveling about an upright axis offset from the longitudinal centerline of said truck at the side thereof remote from said deck between a forwardly facing position and a position facing towards the side of said truck having said deck, fixed partcircular track means centered on said axis for supporting the side of said mast structure further from said axis during said swiveling said mast structure comprising a first guide which, when said mast structure is in said sideways facing position, is disposed in said well, which terminates above the level of said axle and which is fixed against movement in a vertical direction, a second guide which is guided for movement up and down along said first uide, a carrier frame which is guided for movement up an down along said second guide, a

single-extension jack for actuating the movement of said second guide on said first guide and of said carrier frame along said second guide, said jack having a moving member and a fixed member which is fixed with respect to said first guide, a first guide element mounted on said moving member, a first flexible tension element extending over said first guide element and having opposite ends thereof anchored with respect to said first guide and said second guide, respectively, a second guide element mounted on said second guide, and a second flexible tension element extending over said second guide element and having opposite ends thereof anchored with respect to said first guide and said carrier frame, respectively, thereby to drive said second guide at twice the speed of said moving member of said jack and to drive the said carrier frame at twice the speed of said second guide, the arrangement being such that said carrier frame clears said deck at the same time said second frame clears said axle. 

1. A lift truck having a chassis, steerable wheels at one end of said chassis, a well at the other end of said chassis facing lengthwise of said truck, an axle extending across said well, driving wheels mounted on opposite ends of said axle, a deck extending along one side of said truck at a level just above the tops of said driving wheels, a mast structure mounted for swiveling about an upright axis offset from the longitudinal centerline of said truck at the side thereof remote from said deck between a forwardly facing position and a position facing towards the side of said truck having said deck, fixed partcircular track means centered on said axis for supporting the side of said mast structure further from said axis during said swiveling said mast structure comprising a first guide which, when said mast structure is in said sideways facing position, is disposed in said well, which terminates above the level of said axle and which is fixed against movement in a vertical direction, a second guide which is guided for movement up and down along said first guide, a carrier frame which is guided for movement up and down along said second guide, a single-extension jack for actuating the movement of said second guide on said first guide and of said carrier frame along said second guide, said jack having a moving member and a fixed member which is fixed with respect to said first guide, a first guide element mounted on said moving member, a first flexible tension element extending over said first guide element and having opposite ends thereof anchored with respect to said first guide and said second guide, respectively, a second guide element mounted on said second guide, and a second flexible tension element extending over said second guide element and having opposite ends thereof anchored with respect to said first guide and said carrier frame, respectively, thereby to drive said second guide at twice the speed of said moving member of said jack and to drive the said carrier frame at twice the speed of said second guide, the arrangement being such that said carrier frame clears said deck at the same time said second frame clears said axle. 